1. Field of the Invention
The present invention relates to crash stops which park the read-write heads near the disk pack spindle in a Crash Start/Stop (CSS) hard disk drive.
2. Background Information
Modem hard disk drives include a servo controller driving a voice coil which acts upon an actuator assembly to position a read-write head near a track on a rotating disk surface. The read-write head communicates with the servo controller, providing feedback, which is used in controlling the read-write head's positioning near the track. The read-write head is embedded in a slider, which floats on a thin air bearing a very short distance above the rotating disk surface.
A voice coil motor assembly typically includes a voice coil, which swings at least one actuator arm in response to the servo controller. Each actuator arm includes at least one head gimbal assembly typically containing at least one slider. The head gimbal assembly couples to the actuator arm in the voice coil motor assembly.
A hard disk drive may have one or more disks. Each of the disks may have up to two disk surfaces in use. Each disk surface in use has at least one associated slider, with the necessary actuator arm. Hard disk drives typically have only one voice coil actuator. The disk(s) rotates about the spindle motor hub, which contains all of the disks.
When the hard disk drive is not in operation, industry practice is to park the actuator arms holding the read-write heads either near the spindle motor hub or away from the spindle motor hub. This practice evolved as a way to minimize contact and collision damage between the read-write head(s) and the disk surface(s). This invention relates to hard disk drives, which park the read-write heads near the spindle motor hub. These hard disk drives are often known as “Crash Start/Stop” or CSS hard disk drives.
Some hard disk drives use the other crash stop mechanism, parking the read-write heads away from the spindle motor hub, essentially outside the disk diameter. These are sometimes referred to as OD or “Outside Diameter” hard disk drives.
Both crash stop mechanisms must prevent damage to the actuator assembly, particularly the read-write heads, by withstanding rotary shocks in the plane of the disks. Today hard disk drives must withstand rotary shocks of radial shock strength lasting one or more milliseconds. The radial shock strength is often 30,000 radians per second per second.
There is a problem with existing magnetic latching mechanisms used in CSS hard disk drives. The latching mechanism commonly used is a magnetic contact latch, which requires a strong initial releasing force to unpark the actuator assembly. This strong initial releasing force may be 100 to 120 grams of force. Magnetic contact latches require this strong initial releasing force only for a brief distance to unpark the actuator assembly. This requirement creates control difficulties immediately after the initial release of the actuator assembly. The actuator assembly swings hard and fast at first. Time and energy are lost bringing the actuator assembly motion under control. What is needed is a latching mechanism for a CSS hard disk drive meeting the rotary shock requirement, while requiring much less initial releasing force.